* {
    padding: 0;
    margin: 0;
}

li {
    list-style: none;
}

#game {
    position: relative;
    width: 100%;
    height: 600px;
    background-image: url('./images/sky.png');
    overflow: hidden;
}

.bird {
    position: absolute;
    left: 50%;
    top: 235px;
    margin-left: -15px;
    width: 30px;
    height: 30px;
    background-image: url('./images/birds.png');
    transition: top .3s linear;
}

.start {
    position: absolute;
    left: 50%;
    top: 295px;
    margin-left: -100px;
    width: 200px;
    height: 60px;
    line-height: 60px;
    text-align: center;
    font-weight: bolder;
    transition: all .3s ease-in-out;
    cursor: pointer;
}

.start--white {
    font-size: 24px;
    color: #fff;
}

.start--blue {
    font-size: 36px;
    color: #09f;
}

.score {
    position: absolute;
    left: 50%;
    transform: translateX(-50%);
    font-size: 24px;
    color: #fff;
    font-weight: bolder;
    user-select: none;
    z-index: 1;
    display: none;
}

.mask {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(0, 0, 0, .7);
    z-index: 1;
    display: none;
}

.end {
    position: absolute;
    left: 50%;
    top: 70px;
    transform: translateX(-50%);
    text-align: center;
    z-index: 2;
    user-select: none;
    display: none;
}

.end .over {
    font-weight: bolder;
    font-size: 35px;
    color: #f00;
}

.end .result,
.end .final-score {
    margin-top: 20px;
    color: #ff0;
    font-size: 20px;
    font-weight: bold;
}

.end .rank-list {
    margin-top: 20px;
    color: #09f;
    text-align: left;
}

.end .rank-item {
    height: 30px;
    line-height: 30px;
    margin-bottom: 10px;
    padding: 0 10px;
    font-size: 13px;
}

.end .rank-item::after {
    display: block;
    content: '';
    clear: both;
}

.end .rank-item>span {
    display: inline-block;
    vertical-align: middle;
}

.end .rank-degree {
    width: 14px;
    height: 14px;
    line-height: 14px;
    margin-right: 10px;
    text-align: center;
    background-color: #8eb9f5;
    color: #fff;
    font-size: 12px;
}

.end .rank-degree.first {
    background-color: #f54545;
}

.end .rank-degree.second {
    background-color: #ff8547;
}

.end .rank-degree.third {
    background-color: #ffac38;
}

.end .rank-score {
    width: 30px;
}

.end .rank-time {
    white-space: nowrap;
    text-overflow: ellipsis;
    overflow: hidden;
    cursor: pointer;
}

.end .restart {
    color: #09f;
    font-size: 18px;
    font-weight: bolder;
    cursor: pointer;
}

.pipe {
    position: absolute;
    width: 52px;
    background-color: rebeccapurple;
}

.pipe--up {
    top: 0;
    background-image: url('./images/pipe2.png');
    background-position-y: bottom;
}

.pipe--down {
    bottom: 0;
    background-image: url('./images/pipe1.png');
}